1. Field of the Invention
Coal represents approximately 84 percent of the known recoverable fossil fuel resources in the United States; while petroleum and natural gas account for about 10 percent and shale oil for the remaining 6 percent.
The shrinking petroleum and natural gas reserves around the world, and recently enacted governmental sulfur oxides emission standards in the United States, have capsuled the need to focus attention on coal conversion technology and the production of synthetic fuels therefrom to meet the growing demand for energy in the United States and around the world. However, in the production of synthetic fuel, a substantial portion of the fuel is lost in the separation phase, particularly the phase wherein, tar and solid particles are separated therefrom. Normally, during the separation step of a coal liquefaction process, asphaltenes, resins and aromatics are separated along with the tar from the synthetic fuels. Upgrading of the tar product to produce additional synthetic fuel is difficult because the asphaltenes hinder access of the product to catalyst surface normally utilized in an upgrading process. Accordingly, it is desirable to remove the asphaltenes, resins and aromatics from the tar products and subject them to conventional cracking processes before the upgrading step in the process to increase the yield of synthetic fuel which would otherwise not be recovered from the tar products. In the present process, the coal liquefaction products are contacted with a halogenated aliphatic solvent, defined more specifically hereinafter.
2. Description Of The Prior Art.
The separation of dispersed solids from organic liquids, for example hydrocarbons; is known and appreciated in the prior art. For example, in the conversion and upgrading of solid carbonaceous materials (i.e. coal, etc.) into liquid hydrocarbons, tremendous quantitites of the hydrocarbons are produced which contain unreacted coal, ash particles and the like. One method of removing dispersed solids from organic liquids is disclosed in U.S. Pat. No. 3,563,885, entitled Removal of Dispersed Solids From A Liquid, issued to Talbot, on Feb. 16, 1971. The reference relates to the removal of dispersed solids from organic liquids by adding a small quantity of ultra high molecular weight polyethylene under agitation and at an elevated temperature to the liquid. The mixture is allowed to cool until the polyethylene containing the dispersed solids coagulates. The coagulated material is next removed by conventional techniques.
Another approach for separating liquid hydrocarbons from mineral solids is set forth in U.S. Pat. No. 3,941,679, entitled Separation of Hydrocarbonaceous Substances From Mineral Solids, issued to Smith et al, on Mar. 2, 1976, which discloses a method for separating liquid hydrocarbons from the mineral solids of tar sands, oil shales and similiar geological composites. In particular, liquid trichlorofluoromethane is used to dissolve and extract the hydrocarbons from the mineral solids. The references fail, however, to disclose or suggest a process for increasing the yield of synthetic fuels produced from a coal liquefaction process by extracting asphaltenes, resins and aromatic compounds from tar and solid particles previously separated from the coal liquefaction products and upgrading the extracts to produce additional fuel.